1. Field of the Invention
The present invention relates to a method for transferring data packets in a network of user stations, the data packets being transferred over a set of channels with the frequency-hopping method and the channels being in this context selected for data transfer in accordance with a frequency-hopping pattern in temporally successive time slots, and there being assigned to a user station time slots in which it is authorized to transmit.
2. Related Art
A method of this kind is known from DE 44 07 544 A1.
The known method is used to transfer data packets in an auxiliary network which transmits via frequency channels that are at least in part already used in an existing basic network for digital data and/or voice transfer. With this method, in a first step a frequency channel not currently occupied by the basic network is identified, whereupon in a second step a data packet is transferred over the identified frequency channel. These steps are repeated, using frequency-hopping technology, until all the data packets of a transmission have been transferred.
With the known method, by using frequency-hopping technology it is possible to utilize existing channels better without disturbing the respective basic network.
As is common in frequency-hopping technology, the individual data packets are transferred, in accordance with a frequency-hopping pattern, in temporally staggered time slots over various frequency channels, the load being evenly distributed among the available channels.
The underlying frequency-hopping table is in this instance generated pseudo-randomly, the target address being incorporated into the channel calculation. In a specific time slot, only one specific user station is addressed over the particular channel, the assignment of the channels to the user stations being thereby predefined.
With this method, the selection of a frequency channel not currently occupied by the basic network takes place in such a way that one of the multiple frequency channels is first selected, whereupon this selected channel is then listened in on to check whether the basic network is currently transmitting on that frequency channel. If no signal is received during this listening-in process, it is assumed that this channel can be used by the auxiliary network.
If it is found, however, that the selected channel is currently being used by a primary user, the time slot elapses unused, i.e. no data packet is transferred over the selected channel so as not to disrupt the primary user.
It is apparent from the above that with the known method, transmission authorization is permanently allocated to the user stations, so that the number of user stations governs how often a user station can transmit within a specific time span. If some of the user stations have no need to transmit, data throughput with the known method can therefore be greatly reduced due to the unused elapsed time slots.
The assignment of the individual channels of the frequency-hopping pattern to the respective user stations therefore depends on the number of user stations. If their number increases or decreases, the data throughput of an individual user station rises or falls correspondingly.
In addition to the non-optimum data throughput already mentioned above which occurs under certain network conditions, the known method thus has the further disadvantage that data transfer is not always possible in real time. The time intervals in which a user station can transfer its data packets depend greatly on the configuration of the network of user stations.